Process for the gasification of solid carbonaceous materials



Jan. 5, 1954 UK 2,665,200

M. KWA PROCESS F'OR THE GASIFICATION OF SOLID CARBONACEOUS MATERIALSFiled July l, 1948 i Q n \1 il i `1 B 5 xq u Q a. A

(n LL INVENTOR.

Patented Jan. 5, 1954 PROCESS FOR THE GASIFICATION OF SOLID CARBONACEOUSMATERIALS Monson Kwauk, New York, N. Y., assigner to HydrocarbonResearch, Inc., New York, N. Y., a corporation of New Jersey ApplicationJuly 1, 1948, Serial No. 36,314

6 Claims. (Cl. 48-197) rlhis invention relates to the gasiiication of asolid carbonaceous material. In one of its more specic aspects itrelates to carbonization oi coal. The process of the invention isapplicable to gasioation of coal, lignite, oil shale and the like. It isparticularly1 useful for treatment of those carbonaceous materialscontaining volatile constituents which tend to agglomerate on heating,for example, coking coals.

The fluidized solids technique has been applied to processes for thegasification of carbonaceous materials. For example, coal infinely-divided form may be treated in a fluidized bed with hot inertgases to effect removal of volatile constituents or with an oxidizinggas for gasification to any desired extent. Fuid bed gasification isparticularly adapted to gasication of coke or hard coal, such asanthracite, which does not 'tend to agglomerate on heating. Coal may betreated prior to gasication to prevent agglomeration. Such pre-treatmentmay consist of heating the coal to drive off a portion of the volatileconstituents therefrom or partial pre-oxidation of the coal with anoxygen-containing gas, nitric acid, or other oxidizing agent. Anexpedient which is used to some extent involves adu mixing the raw coalwith char, ash, or sand to prevent agglomeration of the raw coalparticles. The process oi the present invention avoids the difficultiesattendant upon these various methods bf handling the coal and provides amethod whereby coal may be charged directly to the gasiiier. There is noproblem of separating inert material from the residual solid materialresulting from the gasication.

The process of the present invention is useful for carbonization ofcoal, or partial gasification, as well as for complete gasification.Gasification of carbonaceous materials containing volatile constituentsmay be accomplished by heating, by chemical reaction, or by acombination or both. In carbonization, the volatile constituents aredriven off by heat to produce a char or coke residue. Gasication bychemical reaction may be carried to substantial completion leaving onlyash or low carbon content char as the residual solid. Elevatedtemperatures are required for gasification, as is known in the art. Thepresent process is applicable to numerous gasification proceduresincluding dry distillation, or carbonization, and reaction with agasifying reactant, e. g., free oxygen, steam, carbon dioxide, hydrogen,or a suitable mixture of these gases.

In accordance with this invention, a bed of particles of vsolid inertmaterial of relatively uniform particle size and having relatively highsettling rates is fluidized by the action of a stream of a suitable gaspassing upwardly therethrough in a gasication zone. The velocity of theiiuidizing gas is such that the fluidized bed of inert material isstationary (like a stationary wave) and substantially no particles ofinert material are entrained by the upflowing stream of gas. This bedmay be properly referred to as a luidized mixed bed oi particles ofsolid inert material.

Solid carbonaceous material in particle form is added to he fluidizedxed bed in the gasication zone. The carbonaceous material is of aparticle size such that it has a lower settling rate than the particlesof inert solid. The carbonaceous material may be conveniently suppliedto the bed by suspension in the fluidizing gas. Ii the iiuidized iixedbed of inert particles were not present in the gasification zone, theparticles of carbonaceous material would be entrained in the gas streamand quickly carried from the gasication zone.

However, due to the resistance oiered by the particles of inert materialthe residence time of the particles of carbonaceous material in thegasification zone is considerably lengthened. The situation is somewhatanalogous to the passage of a gas through a porous medium where themolecules of gas are representative of the fluidized particles ofcarbonaceous material, and the porous medium, the iiuidized bed of theinert material. By carefully controlling the velocity of the uidizinggas, the bed of inert material can be permanently kept in thegasification zone as a iluidized fixed bed while a stream of uidizedcarbonaceous material passes through the openings of the fluidized fixedbed of the inert material in the gasication zone. 4

The fluidized iixed bed of inert solid material aids in maintaining therequired temperature conditions within rather close limits because itincreases the thermal conductivity and thermal stability of the entirebed.

The solid inert material is of a particle size suitable forfluidization, generally less than onequarter inch in average diameterand preferably less than about one-tenth inch in diameter. In general,the particle size of the carbonaceous material will be somewhat lessthan that of the inert material but in some instances, it may begreater.

The composition of the fluidizing gas depend largely upon the type ofgasification carried out.

For dry distillation of coal, an inert gas is used or less permanently.

as the fluidizing medium. For gasification under reaction conditions, agaseous reactant is most suitably included in the uidizing medium. Theresulting gaseous products are Withdrawn from the bed together withentrained particles of residual solid material. The solid particles areseparated from the product gas either as a product char or ash.

The inert solid particles maintain the dispersion of coal particles inthe reactor while at the same time providing all of the advantages of aiiuidized bed. By the process of this invention it is possible to treatan agglomerating coal under gasication conditions in the fiuidizedstate. Thus materials which have heretofore been unsuited to gasicationin a fluidized bed may now be so treated.

Previous attempts at gasication of agglomerating coals and the like in afluid bed reactor have generally involved admixing the raw coal with theresidual solid, such as char or ash. With such an arrangement it isnecessary to handle large quantities of residual solid which has undulycomplicated the required equipment and resulted in high costs ofoperation.

The presence of the inert solid material introduces the combined actionof dispersion, attrition, and comminution on the carbonaceousmaterial-an action which reduces the chance of the carbonaceousparticles contacting one another and forming aggregates. Should anaggregate form, however, it is soon disintegrated by the last twoactions of attrition and comminution. This specific characteristicattendant to the presence of the inert particles makes the processapplicable to the carbonization and gasiiication of carbonaceousmaterials which would normally agglomerato.

As mentioned above, the inert material consists of particles having ahigher settling rate than the carbonaceous material for reaction. A highsettling rate implies a larger particle Weight. Therefore, when inmotion, these particles possess a higher kinetic energy, and are moreeiective in the dispersing and attritive actions than re-circulatedresidue, which, as a rule can be considered similar or smaller in sizeand lighter in weight than the material under reaction. As the bed ofthe inert material is of a stationary nature, i. e., it is not removedfrom the gasification zone, it resides in the vessel more Thiseliminates many costly items of equipment and operational diillcultiesassociated with circulating ash or heat carrier as in prior artprocesses.

The inert solid material can be chosen to have a .high thermalconductivity and speciiic heat.

Thus the distribution, addition, and removal of heat from the bed as awhole can be greatly facilitated. The danger of forming hot-spots ispractically eliminated. Also, the thermal condition of the bed isrendered more stable, inasmuch as it possesses an increased overall heatcapacity for withstanding sudden changes in thermal load.

An object of this invention is to provide an improved process for thegasication of solid carbonaceous material.

Another object is to provide a process for the gasification of solidcarbonaceous material which vv.is particularly applicable` tocarbonization and gasification of coal, lignite, oil shale and similar lmaterials.

` Still another object is to provide .a process for the gasication ofsolid carbonaceous materials may take any of various forms.

which tend to soften and agglomerate on heating.

Other objects and advantages will be apparent from the followingdetailed description and the accompanying illustrative drawings.

The present invention will be described in detail ywith reference tocoal as the carbonaceous material as typifying the operation andapplications of the process of this invention. It will be understoodthat coal is used as a specic example and that the apparatus and methoddescribed are not limited to the use of Coal as the carbonaceous feedmaterial. Since the gasification of various materials is known in theart, the application of the present invention to other solidcarbonaceous materials will be evident to one skilled in the art fromthe detailed description of this invention and illustrative examples ofits application to treatment of coal.

The accompanying drawing is a diagrammatic elevational view illustratingthe process of the present invention.

With reference to the drawing, coal, for example, is fed through line Iinto a hopper 2. An inert gas may be supplied to the hopper through line3 to build up pressure in the hopper. The gas also forms an inertblanket avoiding explosion hazards. The particulate coal is fed from thehopper through a valve 4, suitably a rotary valve conventional forhandling solids, into a stream of fluidizing gas in line E. The powderedcoal dispersed in the iluidizing gas passes through line B to a reactorl into contact with a iluidized bed of inert solid particles 8maintained under gasifying conditions.

The inert solid particles are iluidized by the gas passing upwardlytherethrough. The particles of inert solid material have a highersettling rate than the particles of coal undergoing gasication, that is,the inert particles are of greater density, or larger particle size, orboth. The coal particles are dispersed in the fluidized bed, and broughtrapidly to reaction conditions. As the coal particles pass upwardlythrough the bed they are gasied to the desired extent.

The relative proportions of coal and inert particles in the reactor mayvary considerably but preferably the inert solid particles are presentin excess. For example, from one to ten parts of inert solid may bepresent per part of coal, the larger relative proportions beingpreferred.

'Ihe particles of residual solid material resulting from the gasicationare entrained in the effluent gas stream and carried overhead from thereactor 1 through line I0 with the eiiluent to a separator I I. Theresidual solid material is separated from the gas and discharged fromthe separator through line I2. The resulting gas passes through line I3for a further treatment or utilization in other processes. A portion orall of the fluidizing gas may be a recycle gas separated from the gasstream discharged through line I3. This recycle gas, which preferably isa selected fraction of the gas discharged through line I3, is suppliedto line 6 through a recycle gas line I5. A portion or all of theuidizing gas may be supplied from an outside source through line I6 asdesired.

Heat may be supplied to the reactor from an outside source by means of asuitable furnace I8. Hot gases are Supplied to the furnace through ductI9 and the residual flue gases discharged through duct 20. Furnace I8 isoptional and The furnace is useful for dry distillation of thecarbonaceous material and for endothermic reactions, e. g..

5 with steam or carbon dioxide. When free oxygen or hydrogen is suppliedto the reactor for chemical reaction with the carbonaceous material,furnace I8 may be unnecessary.'

When the particles of coal are brought intol 'the particles of coal andwhere heat is transferred by indirect heat exchange facilitates the heatexchange between the particles of coal and the hot metal surfaces.

The carbonaceous particles mix readily in a mechanical way with theadded solid particles. However, since the inert solid has a highersettling rate than the carbonaceous particles, the latter work steadilyupward through the fluidized bed. Under these conditions the residualsolid particles from the carbonaceous material are selectivelyeliminated from the fluidized bed and carried out of the reactor by theefliuent gases. Thus by choice of an inert material of requisite sizeand density, relative to the size and density of the carbonaceousparticles, the relative proportions of carbonaceous material and inertmaterial in the iiuidized bed is readily ccntrclled. The fluidizing gasmay be made up sclely of inert gas or may comprise gaseous reactantsutilized in the reactor for gasification of the solid carbonaceousmaterial.

In the carbonization of coal, for example, a hydrocarbon gas which isinert with respect to the distillation products is most suitably used asthe fluidizing gas. This may comprise methane and other gases includinglight hydrocarbons resulting from the distillation of the coal itself.Often it is desirable that the fluidizing gas contain some Water Vaporto prevent deposition of carbon on the inert material.

The temperature of the distillation is suitably within the range of llto l300 F., and the pressure, from atmospheric to about 60 pounds persquare inch gauge.

The luidizing gas may be at an elevated temperature prior to contactwith the coal sufficient to supply part or all of the heat ofdistillation. The remaining heat is supplied by furnace lil to thefluidized bed by indirect heat exchange through the Wall of the reactorl. The inert solid material having a higher thermal conductivity thanthe carbonaceous material enhances the rate of heat transfer from theWalls of the reactor to the solid carbonaceous material undergoingtreatment.

The distillation products withdrawn through lines it and i3 may betreated to separate the normally liquid coal tar hydrocarbons and tar. Aportion of the normally gaseous fraction of the volatile constituents,comprising principally methane, may be recycled through line I as thefluidizing gas. In this case it is not necessary to supply gas throughline le.

When the present process is operated, for example, for gasication ofcoal by reaction with free oxygen to produce either synthesis gas orproducer gas, the iiuidizing gas comprises free oxygen and steam.Methane, tail gas from the synthesis reaction, or the like may be usedto supplement the primary reactants. The gases lib- ,leased may beadmixed, where permissible, or introduced separately into the reactor.With free oxygen as a reactant it is generally not necessary to supplyheat from an outside source due to the exothermic nature of theoxidation reaction. Steam and carbon dioxide enter into endotherrnicreactions with heated carbon. Heat rein the exothermic reaction may beutilized by these endothermic reactions. By choosing conditions suchthat a proper balance is attained, the process may be madeself-sustaining on a heat basis. Gasiiication with oxygen land steam isgenerally carried out at 1800 to 2000 F. at pressures up to about 400pounds per e square inch gauge.

The inert material aids in the heat transfer between the exothermic andendothermic reactions. The heat released by the exothermic reactiontaking place upon introduction of the reactants into the reactor, e. g.,burning of the vcoal to form carbon dioxide and Water, is rapidlytransmitted by the inert material in the uid bed to carbon throughoutthe bed. Thus there is e'cient heat transfer to the reactants in thatportion of the reactor where carbon dioxide and water vapor react withcarbon. These endothermic reactions take place subsequent to the initialoxidation reaction and at a point removed from the point of introductionof oxygen to the reactor.

Entirely endotherinic reactions may be carried out in the reactor, forexample, reaction of hot carbon with steam or carbon dioxide. Part orall of the heat requirements for such reactions may be supplied by heatexchange as in the case of distillation. lt is generally preferable tosupply at least a part of the heat required for the endothermic reactionby preheating the reactants. The inert material aids the transfer anddistribution of heat to the gases and solid carbonaceous reactants,

The inert solid material employed is subject to considerable variationin choice. The following general conditions may be set as determiningfactors in selecting the inert solid material. The average size of theinert particles should be of about the same order of magnitude as thecarbonaceous particles; preferably the inert particles are larger. Thedensity of the inert particles should be higher than that of thecarbonaceous material so that they are retained in the reactor when thevelocity of the lluidizing gas is greater than the average terminalvelocity of the carbonaceous particles. Preferably, the inert materialhas high thermal conductivity and high specific heat. The inertparticles should be refractory and resistant to attrition and spalling.Among the materials which. may be mentioned as suitable for use inaccordance with the process of this invention are smooth compact piecesor pellets of alumina, silica, zirconia, magnesia, compositesI of thesematerials, silicon carbide, high melting point ferrous alloys, and thelike.

The raw carbonaceous solid may be introduced into the reaction zoneseparately from the reactant gas where undesirable preliminary reactionis likely to take place. This may be accomplished by dispensing thecarbonaceous particles in a stream of innocuous gas which may be inertor relatively unreactive under conditions prevailing prior tointroduction of the suspension into the reaction zone. Steam, carbondioxide, and other endcthermic reactants generally fall in the lattercategory and may be premixed with the carbonaceous material.

-Obviouslyxmanyjfmodifications and variations :offthe inventionfashereinabovesetforth may be rceous .material which tends tofagglomerateon sitory mass-of unreactiveasolid contact material .in thepformofparticles having a relatively high settling rate in gaseous suspension,continuously introducing into theilower portion'of said zone vsolidcarloonaceousmaterial in the form of par- -ticles ha-ving a relativelylow settling rate in gaseous suspension, continuously introducing tovthe lower-portion lof said zone a stream of iuidizinggas Which isunreactive with said solid contact ymaterial under conditions prevailingWithin the zone, passing said stream upwardly through said mass ofparticles with sufcient velocity to eiect entrainment of saidparticlesof carbona ceous material and'to maintain said particles of contactmaterial inhighly agitated condition but Without substantial entrainmentof said particles of contact'material, eiecting'substantial gasicationof said solid carbonaceous material during its passage through saidcontact material Within said zone, continuously removing from the upperportion of said zone an effluent stream of gaseous reaction productscontaining entrained residual solid material resulting from gasificationof said solid carbonaceous material.

'2. A process as defined in claim l wherein the solid carbonaceousmaterial is coal.

3. A process as defined in claim 1 wherein the luidizinggas comprises agas reactive with the solid carbonaceous material.

4. A'process vas'dened in claim 1 wherein the fluidizing gas comprises agas'selected from the group consisting of oxygen, hydrogen carbondioxide and steam.

5, In a process for vtreating a solid carbonaceous material toeiect"gasication thereof in a gasiiication izone, the improvementcomprising f disposing within said zone' a substantially nontransitorymass of unreactivel solid contact material in the form of particleshaving a'relatively high settling rate inigaseous suspension,continuously introducing into the lower portion of said mass solidcarbonaoeous material in the form of 'particles having a relatively lowsettling rate 'in gaseous suspensiony supplying heat to said reactionzone from an external source by heat transfer through a wall of saidreaction zone to said mass of particles contained therein, continuouslyintroducing into the lower portion of said zone a stream of fluidizinggas which is unreactive with said solid contact material underconditions prevailing Within said Zone, passing said stream upwardlythrough said mass of particles with sufficient velocityto eiectentrainment of said particles of carbonaceous material and to maintainsaid particles of contact material in highly agitated condition butwithout substantial entrainment of said particles of contact material,effecting substantial gasiication of said solid carbonaceous materialduring its passage through said contact material within said zone,continuously removing from the upper portion of said zone an eiiluentstream of gaseous reaction products containing entrained residual solidmaterial resulting from gasification of said solid carbonaceousmaterial.

5. A process as defined in claim 5 wherein said solid carbonaceousmaterial is a caking coal.

MOOSON KWAUK.

References Cited in the file 0f this patent UNITED STATES PATENTS NumberName Date 1,873,941 Hillebrand -Aug. 23, 1932 2,443,673 Atwell June 22,1948 FOREIGN PATENTS Number Country Date 321,422 Great Britain Nov. 4,1929 586,391 Great Britain Mar. 18, 1947 OTHER REFERENCES Lange,Handbook of Chemistry,`5th Edition, pp. 1374-1375.

1. IN THE PROCESS FOR TREATING A SOLID CARBONACEOUS MATERIAL WHICH TENDSTO AGGLOMERATE ON HEATING TO EFFECT GASIFICATION THEREOF IN AGASIFICATION ZONE MAINTAINED UNDER GASIFICATION CONDITIONS, THEIMPROVEMENT WHICH COMPRISES DISPOSING WITHIN SAID ZONE A SUBSTANTIALLYNON-TRANSITORY MASS OF UNREACTIVE SOLID CONTACT MATERIAL IN THE FORM OFPARTICLES HAVING A RELATIVELY HIGH SETTLING RATE IN GASEOUS SUSPENSION,CONTINUOUSLY INTRODUCING INTO THE LOWER PORTION OF SAID ZONE SOLIDCARBONACEOUS MATERIAL IN THE FORM OF PARTICLES HAVING A RELATIVELY LOWSETTLING RATE IN GASEOUS SUSPENSION, CONTINUOUSLY INTRODUCING TO THELOWER PORTION OF SAID ZONE A STREAM OF FLUIDIZING GAS WHICH ISUNREACTIVE WITH SAID SOLID CONTACT MATERIAL UNDER CONDITIONS PREVAILINGWITHIN THE ZONE, PASSING SAID STREAM UPWARDLY THROUGH SAID MASS OFPARTICLES WITH SUFFICIENT VELOCITY TO EFFECT ENTRAINMENT OF SAIDPARTICLES OF CARBONACEOUS MATERIAL AND TO MAINTAIN SAID PARTICLES OFCONTACT MATERIAL AND TO MAINTAIN SAID PARTICLES OF WITHOUT SUBSTANTIALENTRAINMENT OF SAID PARTICLES OF CONTACT MATERIAL, EFFECTING SUBSTANTIALGASIFICATION OF SAID SOLID CARBONACEOUS MATERIAL DURING ITS PASSAGETHROUGH SAID CONTACT MATERIAL WITHIN SAID ZONE, CONTINUOUSLY REMOVINGFROM THE UPPER PORTION OF SAID ZONE AN EFFLUENT STREAM OF GASEOUSREACTION PRODUCTS CONTAINING ENTRAINED RESIDUAL SOLID MATERIAL RESULTINGFROM GASIFICATION OF SAID SOLID CARBONACEOUS MATERIAL.